Condition responsive systems

ABSTRACT

A plurality of condition responsive systems are disclosed which respond to one or more diverse conditions such as the insertion of a plug into a power receptacle and/or the signal from a thermally responsive device to control a switching device in response thereto.

' United States Patent [1 1 [111 3,913,046

Davis et al. Oct. 14, 1975 CONDITION RESPONSIVE SYSTEMS [56] References Cited [76] Inventors: Claude A. Davis, 568 Piney Forest UNITED STATES PATENTS R Joseph L- S d g, 2500 3,020,423 2/1962 Gerber 310 s.9 'Riverside Drive, both of Danville,

24541 Primary ExaminerL. T. l-lix [22] Filed: Oct 9, 3 Assistant Examiner-Fred E. Bell Attorney, Agent, or FirmAnthony A. OBrien [21] Appl. No.: 404,688

Related U.S. Application Data [57] ABSTRACT Continuation-impart Of 581 232,597, March A plurality of condition responsive systems are dis- 1972- closed which respond to one or more diverse conditions such as the insertion of a plug into a power re- [52] U.S. Cl; 337/13; 317/235 M; 337/3 ceptacle d/ the signal f a thermally responsive [51] Int. Cl. H01 31/00; HOll-l 61/00 device to Control a switching device in response 58 Field of Search 317/235 M, 144; 337/3, thereto 35 Claims, 11 Drawing Figures U.S. Patent 0ct.14,1975 sheetlom 3,913,046

US. Patent Oct.14,1975 Sheet2of4 3,913,046

US. Patent Oct. 14,1975 Sheet 3 of4 own Nwm

mom m5 vmm U.S. Patent 0t.14,1975 3mm 3,913,046

CONDITION RESPONSIVE SYSTEMS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 232,597 filed Mar. 7, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to condition responsive systems, and more particularly, to condition responsive systems which control a switching device in response to a thermal condition and/or the insertion of a receptacle plug.

2. Description of the Prior Art The prior art, as exemplified by U.S. Pat. Nos. 2,500,474; 2,531,625; 2,540,496; 2,735,906; 2,826,652; and 3,370,141, is generally cognizant of power receptacles which have a switch controlled in response to plug insertion and/or removal. However, all known prior art devices are constructed with the contact structure of the receptacle functioning as part of the switching device. This results in a complex and unique assembly in which important design criteria pertaining both to the power receptacle and the switch are comprises in order to obtain the desired composite structure.

The prior art, as exemplified by US. Pat. No. 3,320,601, is also aware of the use of thermally responsive devices, such as bimetals, to control the state of a switch and a utilization device which responds to the switch state to effect a control or alarm function. However, in the use of such systems, the switch contacts are usually positioned directly by the bimetal or through the intermediary of mechanical linkage, requiring a sizable movement of the bimetal and/or associated linkage to change the state of the switch and, accordingly, control the utilization device. Such prior art systems have not proven to be completely satisfactory in operation, exhibiting erratic switching with advancing age and a high failure rate.

SUMMARY OF THE INVENTION The present invention is summarized in a thermally responsive system including thermal element means having a fixed portion and a portion movable in response to a thermal condition, and piezoelectric crystal means adjacent the movable portion of the thermal element means and capable of producing a signal in accordance with pressure applied thereto by the movable portion.

An object of the present invention is to construct a high sensitivity thermal sensor.

Another object of this invention is to produce a limited movement thermal sensor employing a pressure responder.

A further object of this invention is to accurately and reliably operate a control circuit in response to thermal stimulation.

Yet another object of the present invention is to provide a load current protection system employing the thermal sensor as a load current conductor.

Still another object of this invention is to construct an alarm system including a high sensitivity thermal sensor.

Another object of this invention is to actuate a switching-device in response to plug insertion.

An advantage of the present invention over the prior art are that the mechanical movement which occurs in response to thermal variation can be considerably reduced, reduction in sensitivity.

Other objects and advantages of the present invention will be more fully apparent from the following description of the preferred embodiments when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial elevational view of a receptacle according to the present invention;

FIG. 2 is a side elevational view, paritally in section, of the receptacle of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2 showing one embodiment of the receptacle of the present invention in one operative position;

FIG. 4 is a sectional view of the receptacle of FIG. 3

with parts shown in another operative position;

FIG. 5 is a sectional view similar to FIG. 3 showing another embodiment of the receptacle of the present invention in one operative position; and

FIG. 6 is a sectional view of the receptacle of FIG. 5 with parts shown in another operative position;

FIG. 7 is a side elevation view, partly in section and partly schematic circuit diagram, of a thermally responsive control system according to the present invention;

FIG. 8 is a side elevation view, partly in section and partly schematic, of another embodiment of a thermally responsive control system;

FIG. 9 is a schematic circuit diagram of a relay system which may be utilized in the embodiments of FIGS. 7 and 8;

FIG. 10 is a schematic circuit diagram of another embodiment of a relay system which may be utilized in the embodiments of FIGS. 7 and 8;

FIG. 11 is a side elevation view, partly in cross section and partly schematic circuit diagram, of a heating control system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, a preferred embodiment of a connection responsive power receptacle according to the present invention is shown generally at 10 in its operative position within a conventional wall-box 12 mounted flush with the exposed surface of a wall 14. A cover plate 16 is secured to the receptacle 10 by any suitable means such as a screw 18 to close the wall-box 12 and complete the installation. I

Receptacle 10 includes a main body member 20 having a pair of contact terminals 22 and 24 which are connected by lines 26 and 28, respectively, to a source of alternating current represented schematically by terminals 30. Affixed to a rear surface of body member 20 is a single-pole, single-throw switch 32 which is responsive to insertion and removal of a conventional power plug 34 as will be described more fully below. A second switch 36 also may be affixed to the rear surface of body member 20, as shown, if desired.

Referring to FIGS. 3 and 4, body member 20 includes a pair of spaced, parallel plug-prong receiving slots 38 and 40 and a pair of contact blades 42 and 44 which are partially folded over upon themselves to estend laterally into slots 38 and 40, respectively. Contact blades 42 and 44 are electrically interconnected internally of body member 20 with terminals 22 and 24 to feed operating potential from source 30 to plug 34 through a set of plug-prongs 46 and 48.

Slot 38 of body member 20 extends completely therethrough by means of an aperture 50 formed in a rear wall of the body member. As shown in FIGS. 3 and 4, switch 32 has an electrically insulated housing 52 and is mounted onto body member 20 such that an actuating arm 54 of switch 32 extends through aperture 50 into slot 38. Arm 54 is adapted to be engaged by prong 46 of plug 34 and moved linearly thereby along the elongate axis of slot 38. A leaf-spring contact arm 56 is affixed at one end 58 to the switch housing 52 and carries a movable contact 60 at its distal end. A fixed contact 62 is attached to housing 52 for cooperation with movable contact 60. As shown in the drawing, arm 54 engages contact arm 56 at a point near end 58 such that movement of arm 54 into housing 52 causes contact 60 to move away from its normal spring-biased position in engagement with fixed contact 62. A collar 64 on arm 54 prevents the arm from inadvertently becoming dislodged from its operative position within switch housing 52.

In operation, switches 32 and 36 may be connected to any suitable electrical apparatus to be controlled in response to plug insertion and/or removal, such as a burglar alarm (not shown). Also, the receptacle preferably is supported within conventional wall-box 12 such that the exterior appearance thereof resembles that of an ordinary power receptacle as shown in FIG. 1.

Referring to FIG. 3, when a plug 34 is inserted into the slots 38 and 40 of housing 20, arm 54 of switch 32 is engaged by prong 46 and moved linearly thereby such that contact 60 of bimetal 56 is moved away from fixed contact 62 (FIG. 4). The switch thus becomes open to perform the desired control function. If plug 34 is subsequently removed, the withdrawal of prong 46 frees actuating arm 54, and contact arm 56 springs back to its normally-biased position with contacts 60 and 62 engaged (FIG. 3) If, for example, a burglar alarm is connected to switch 32 and the receptacle is used for the television receiver in a motel room, the removal of the television plug will result in the closure of switch 32 and the actuation of the burglar alarm. It can be appreciated, of course, that any number of diverse functions may be performed by the apparatus of the present invention, depending upon the particular application, and the above example is presented solely for purposes of explanation and clarity.

It is noted that receptacle 10 according to the present invention is particularly advantageous in that the switch 32 and the main body member 20 are structurally independent. By this is meant that failure of the switch does not necessitate replacement of the main body member, and vice versa. Also, by constructing the switch 32 separately from the main body member 20, mass-produced standard receptacles may be used for main body member 20 with the minor modification of the forming of aperture 50 in a rear wall thereof. As a result, the receptacle of the present invention is extremely economical and reliable, has a conventional exterior appearance, and does not require complex, unusual contact-switch subassemblies which are inherently disadvantageous.

Referring now to FIGS. 5 and 6, there is illustrated another embodiment of the power receptacle according to the present invention in which electrical power is only supplied to a plug after substantially complete plug insertion, thereby obviating a dangerous electrical shock hazard. For the sake of brevity, parts identical to parts described with respect to the embodiment of FIGS. 3 and 4 are identified with identical numbers and are not described again. Likewise, parts similar to parts in the embodiment of FIGS. 3 and 4 are identified with similar numbers having added thereto.

As shown in FIG. 5, affixed to a rear wall of main body member 20 is a switching device 132 which is connected to one terminal with line 28 from power supply 30 and at its other terminal with a line 170 feeding contact terminal 24 of the main body member 20. Thus, switch 132 is connected in series with the contact blades 42 and 44.

Switch 132 has an electrically insulated housing 152 affixed to a rear surface of body member 20 such that actuating arm 154 extends through aperture 50 for linear movement along the elongate axis of slot 38 by plug prong 46. Actuating arm 154 is slightly shorter than arm 54 of the embodiment of FIG. 3 and, consequently, is not engaged by prong 46 until substantially complete insertion of plug 34 into slots 38 and 40, as shown by the dashed lines in FIG. 5.

A leaf-spring contact arm 156 is attached to housing 152 at one end and carries a movable contact 160 on its free end. A fixed contact 162 is mounted in housing 152 for cooperation with contact 160 to form a normally open, single-pole, single-throw switch. A collar 164 prevents actuating arm 154'from falling out of housing 152. It is noted that actuating arm 154 is located adjacent the fixed end of contact arm 156 such that movement of actuating arm 154 into housing 152 closes contacts 160 and 162.

In operation, switch 132 is normally biased to an open-circuit position such that no power is applied to contact blades 42 and 44 of the receptacle. The receptacle therefore is safe and will not cause electrical shock to children who, because of a lack of appreciation of the dangers involved, might inadvertently insert irnetal objects into slots 38 and 40. However, upon insertion of plug 34 into the receptacle to the position shown by the dashed lines in FIG. 5, prong 46 engages actuating arm 154 and after approximately the last onequarter inch of insertion, switch contacts 160 and 162 become closed to apply from source 30 to both terminals 22 and 24 of the main body member 20 (FIG. 6). Upon plug removal, actuating arm 154 will be freed by the withdrawal of prong 46 and contact am 156 will spring back to its normally-open position as shown in FIG. 5.

Thus, it can be appreciated that the receptacle of the present invention is extremely simple and effectively provides no-shock protection for use especially around small children. It should be understood, of course, that the teachings of this invention may be extended to construct switch 132' as a double-pole, single-throw switch to provide isolation of contact terminal 22 as well as contact terminal 24, if so desired. The other advantages noted with respect to the embodiment of FIG. 3 are also provided by the receptacle of FIGS. 5 and 6 and thus will not be repeated for the sake of brevity.

Referring to FIG. 7, power receptacle 10 is combined with a thermostat assembly, shown generally at 200, including a housing 202 physically attached to wall box 12 by a pair of suitable brackets 204 and 206.

A piezoelectric crystal 208, having a pair of voltagecurrent pickup plates 210 and 212 thereon, is supported within the housing by any suitable means (not shown). Thermal elements 214 and 216, such as bimetal strips, are fixedly supported at one end thereof by respective electrically conductive anchors 218 and 220 and have their other movable end contacting opposite sides of a conductive, U-shaped bracket member 222 disposed about and abutting opposite sides of the piezoelectric crystal 208.

As shown, the thermal elements 214 and 216 have a curved or arcuate configuration, which configuration tends to change in accordance with changes in temperature, tending to either straighten or to assume a greater curvature configuration depending on the magnitude and direction of the temperature changes to which they are subjected. In the present instance, the thermal elements 214 and 216 utilized tend to straighten with increasing temperature, although it should be apparent that the opposite acting thermal elements may also be utilized with appropriate modifications without departing from the spirit of the invention.

The coil 224 of a relay 226 is electrically connected across the respective pickup plates 210 and 212. Relay 226 additionally includes a core 228 of ferromagnetic material disposed within the relay coil 224 and a ferromagnetic armature 230 movable about a pivot 232 to control a pair of relay switch contacts 234 and 236 between open and closed positions by means of an actuator 238 carried by the armature 230. A retract spring 240 is connected between an end of armature 230 and a support member 242 affixed to the ferromagnetic core 228.

Affixed to armature 230 is a non-magnetic reed 244, of slightly flexible construction, disposed in alignment with a movable plunger 246 which extends through an aperture 248 into the housing 202 and adapted to be contacted thereby. A collar 250 is fixedly supported on plunger 246 and a retract spring 252 is connected between the collar 250 and an inner wall of housing 202. Plunger stop tube 254 is disposed about an end of plunger 246 and includes a flanged end 256 located proximate collar 250 which acts to limit the movement of the collar 250 and plunger 246 toward the reed 244, thereby protecting same from damage due to an excessive application of force by plunger 246. The plunger 246 includes a smaller diameter shaft 258 extending through the back of wall box 12 into slot 38 of power receptacle 10. Shaft 258 is alignment with the path of prong 48 of plug 34 as it is inserted into power receptacle and is adapted to be moved thereby. The portion of plunger 246 disposed between the wall box 12 and housing 202 is enclosed by a sleeve 260 attached at its ends to the wall box 12 and housing 202, respectively.

A pair of pressure plates 262 and 264, positioned adjacent opposite sides of piezoelectric crystal 208, are movably supported on respective adjusting screws 266 and 268 which extend through threaded members 270 and 272 out of the housing 202.

Each thermal element 214 and 216 has a pair of thermal load members 274, of thermally conductive material such as metal, disposed adjacent respective sides thereof, which act to drain off some of the heat in the thermal elements 214 and 216 to thereby vary the range of operation and prevent excess pressure on the piezoelectric crystal 208. Each thermal load member 274 is movably supported by a respective adjusting screw 278 which extends through respective threaded members 280 out of housing 202 in similar fashion to adjusting screws 266 and 268. Each of the above adjusting screws 266, 268 and 278 terminates outside the housing 202 in a manual control knob 282.

The power receptacle 10 and thermostat assembly 200 are electrically interrelated to establish a continuous series power circuit therethrough. The power circuit includes a power supply 284 connected between contact terminal 22 of power receptacle 10 and switch contact 234 via conductors 286 and 288, respectively. Switch contact 236 is electrically coupled to thermal element 214 at electrically conductive anchor 218 by a conductor 290, and another conductor 292 connects thermal element 216 to contact terminal 24 of the power receptacle 10 through electrically conductive anchor 220 to complete the circuit.

In operation of FIG. 7 embodiment a load, such as a motor (not shown), to be protected from high current burnout, is connected to the contacts of plug 34. The plug 34 is initially inserted in power receptacle 10 such that a series circuit is completed through power supply 284, thermal elements 214 and 216 through anchors 218 and 220, conductive member 222 and initially closed contacts 234 and 236 of relay 226 through conductors 286, 288, 290 and 292 to energize the motor load.

The pressure plates 262 and 264 have been adjusted to apply an initial pressure to the piezoelectric crystal 208 thereby establishing a residual signal at pickup plates 210 and 212 which may be set to overcome the residual magnetism effect of the relay 226. In addition,

the thermal load members 274 have also been adjusted to the proper spacing from the thermal elements 214 and 216 in aaccordance with the particular conditions to be encountered during operation.

The thermal elements 214 and 216 are initially relaxed in their curved position under low temperature and current conditions and, accordingly, under such conditions are applying little or no pressure to the surfaces of the piezoelectric cyrstal 208. Consequently, the signal generated at the pickup plates 210 and 212 of the piezoelectric crystal 208 in response to the pressure applied by the thermal elements 214 and 216 and the pressure plates 262 and 264 is below the threshold level required to cause actuation of the relay armature 230, and the contacts 234 and 236 maintain their initially closed condition.

In the event of an excessive current condition through the motor and, accordingly, through the thermal elements 214 and 216 in series therewith, the thermal elements 214 and 216 develop a tendency to straighten in response to heat produced by the high current flow therein. However, any straightening is substantially prevented due to the movable ends of the thermal elements being in contact with the sides of the U-shaped bracket member 222, which sides are contacting, or positioned very close to, the surfaces of the piezoelectric crystal 208. Therefore, the tendency of the thermal elements 214 and 216 to straighten will develop a commensurate increase in the pressure applied thereby to the piezoelectric cyrstal 208 through the opposite sides of U-shaped bracket member 222. The increasing pressure causes the signal applied to relay coil 224 from the pickup plates 210 and 212 to increase toward the threshold level of the relay 226. When the threshold level is reached, armature 230 will be attracted to the ferromagnetic core 224 causing the actuator 238 carried thereby to operate on switch contact 236, opening the switch contacts 234 and 236 and thereby terminating the power application to the motor load to protect same from burn-out.

Once the switch contacts 234 and 236 have opened, the lack of current flow through thermal elements 214 and 216 enables them to coll and gradually assume their initial relaxed state, thereby commensurately reducingthe pressure applied to the piezolectric crystal and the level of the signal generated at pickup plates 210 and 212. As the level of the signal from pickup plates 210 and 212 reduces, automatic reset may then occur when the combined pressure applied by thermal elements 214 and 216 and the pressure plates 262 and 264 carried by the respective adjusting screws 266 and 268 is reduced to a level below the holding level for the particular relay utilized. Upon the occurrence of reset, the motor will again be energized by the power supply 284.

In the event that relay 226 fails to automatically reset, either because of malfunction of because the residual signal level from pickup plates 210 and 212 has been set to exceed the holding level of the relay 226, a manual reset may be achieved by allowing the retract spring 252 to retract the plunger 246 away from reed 244 and thereafter extending the plunger 246 back into contact with the reed 244 to impulse same with a sufficient force, as limited by the flanged end 256 of plunger stop tube 254, to retract the armature 230 from the relay core 228. Such can be made to occur by merely removing plug 34 from the power receptacle 10 and thereafter fully reinserting same.

The above described system may also function control a heater load (not shown) with only slight adjustments. The heater load would be connected to the contacts of plug 34 like the motor load, and would be periodically energized and deenergized by the closing and opening, respectively, of the switch contacts 234 and 236 in response to the temperature of the surrounding medium as sensed by thermal elements 214 and 216. When controlling a heater load in such manner, the system would be adjusted to insure automatic resetting such that upon cooling of the thermal elements 214 and 216 the switch contacts 234 and 236 would automatically close to restart a heating cycle by reestablishing current flow through the heater load.

Although the motor or heater load of FIG. 7 is shown to be serially connected to the power circuit through the intermediary of the plug 34 and power receptacle 10, it should be understood that such load can also be connected directly to the power circuit without the use of the plug power receptacle intermediary. This may be accomplished for example, by connecting conductors 286 and 292 directly to the load rather than to contact terminals 22 and 24 of power receptacles 10. Contact terminals 22 and 24 would then be connected directly to a pair of lines from a power supply to thereby energize power receptacle 10 in a conventional manner.

With slight modification the system of FIG. 7 can be converted from an overload responsive system into a One of the circuits includes a power supply 302 coupled directly to contact terminals 22 and 24 of the power receptacle 10 by conductors 304 and 306, respectively. The other circuit includes a power supply 308 connected to switchcontact 234 by conductor 310 and to a control or utilization device 312, such as an alarm, through conductor 314. Anchors 218 and 220 are connected, respectively, to switch contact 236 via conductor 290 and to alarm 312 by conductor 316 to complete a series circuit through the thermal elements 214 and 216. In this embodiment, thermal elements are selected which receive little or no heat due to current flow therethrough, such that they may be primarily responsive to ambient temperature conditions rather than current flow conditions.

In the operation of the FIG. 8 embodiment, initially assuming a normal ambient temperature, the thermal elements are initially relaxed and are applying little or no pressure to piezoelectric crystal 208 through bracket member 222 such that the pickup plates 210 and 212 of the piezoelectric crystal 208 initially produce a signal below the relay threshold level and the relay is initially deenergized, with switch contacts 234 and 236 in their normally open state. In the event of excessive ambient temperature sensed by the thermal elements 214 and 216 they develop a tendency to straighten, increasing the pressure applied to the piezoelectric crystal 208. The signal from the pickup plates 210 and 212 then exceeds the relay threshold level and the contacts 234 and 236 are caused to close, thereby completing the series circuit through the power supply and the control or utilization circuit 312 to trigger an alarm and/or effect a control function in response to the excessive heat.

The resetting of switch contacts 234 and 236 may occur either automatically or manually as described above in the operation of the FIG. 7 embodiment.

FIGS. 9 and 10 show additional embodiments of relay systems which may be employed in place of the relay systems shown in FIGS. 7 and 8. Although the switch contacts 234 and 236 are shown to be separable by the armature in response to actuation of the relay as in FIG. 7, it should be apparent that the armature may be positioned, relative to the contacts, to be compatable in the embodiment of FIG. 8.

In FIG. 9, piezoelectric crystal 208 has its pickup plates 210 and 212 connected to the relay coil 224 wound about ferromagnetic core 228, exactly as in FIGS. 7 and 8, Another coil 340, which is also wound around electromagnetic core 228 in the same direction as relay coil 224 such that the flux generated by the respective coils are additive is connected to a direct current power supply through a variable resistor 342. The direct current power supply which is of a conventionally known type, includes an alternating current supply 344 in series with 'a rectifier diode 346, and a ripple filter capacitor 348 thereacross.

In the operation of the FIG. 9 relay system, the alternating current signal from power supply 344 is rectified by diode 346 and filtered by capacitor 348 resulting in a direct current signal continuously applied to coil 340 having a magnitude which may be pre-set by adjustment of variable resistor 342. Accordingly, an initial flux is generated in core 228 due to the direct current flow through coil 340 which is less than that required to actuate the relay. Since the coil 224 coupled across pickup plates 210 and 212 may also be generating an intial flux aiding the flux from coil 340, due to initial pressure applied by thermal elements 214 and 216 and- /or plates 262 and 264, under normal initial conditions the sum of the fluxes must be less than the threshold flux value required to operate the relay, although it should be apparent that it may be adjusted to a level very closeto the threshold flux value, such that only a slight additional pressure increase caused by the thermal elements in response to a change in current flow therethrough or ambient temperature thereabout will cause the relay to operate.

In FIG. 10, piezelectric crystal 208 has its pickup plates 210 and 212 connected across the end terminals of a center tapped potentiometer 360, one end of which is grounded. The center tap of potentiometer 360 is connected to the grid of an electron tube 362 which has its cathode grounded through a variable resistor 364. The anode of electron tube is connected to the direct current power supply including alternating current power supply 344 rectifier diode 346 and ripple filter capacitor 348, through a series circuit including relay coil 224 and variable resistor 366. As an optional feature, a time delay capacitor 368 may be included in shunt with relay coil 224.

In the operation of the FIG. 10 relay system, the signal from the pickup plates 210 and 212 of piezoelectric crystal 208 is applied to the grid of an electron tube 362 which initially is non-conducting or operating in a low conduction state. Accordingly, the initial current, if any, from the alternating current source 344, as rectified by diode .346 and filter by capacitor 346, which flows through the anode-cathode circuit of the electron tube 362 and the relay coil 224 in series therewith, is such that the fiux in coil 224, if any, is less than the flux threshold level of the relayul-lowever, increased pressure from the thermal elements 214 and 216, in response to increased current fiow therethrough or increased ambient temperature, increases the signal to the grid of electron tube 362, to thereby significantly increase the current flow through the anodecathode circuit thereof and the associated relay coil 224 to thereby actuatethe relay armature and the contacts controlled thereby.

Referring to FIG. 11, a thermostat, indicated generally at 400, includes a housing 402 which may have approximate mounting means (not shown) to facilitiate disposition on a wall or the like.

Piezoelectric crystal 208 is mounted in the housing 402 between thermal elements 214 and 216 which are supported at their fixed ends by anchors 218 and 220, and has its pickup plates 210 and 212 connected to the ends of a center tapped potentiometer 360 which is grounded at one end. A temperature control dial 404, mounted on the housing 402, is mechanically joined to the center tap of potentiometer 360 to facilitate adjustment thereof. The center tap of potentiometer 360 is coupled to the grid of electron tube 362 and the relay coil is connected in the anode-cathode circuit of the electron tube 362as in FIG. 10.

Switch contacts 234 and 236 are serially connected with a gas valve solenoid 406, and the secondary of a transformer 410 energized by alternating current supply 344. The solenoid 406 controls the flow of gas through aflow line 412 to a gas space heater 414.

' In the operation of the system of FIG. 11, assuming the ambient temperature is below its normal level, the heater 414 is burning gas moving through gas line 412 due to the valve controlled by solenoid 406 being in its open position. The curved thermal elements, which were initially relaxed in response to the cool ambient temperature, tend to straighten and apply a gradually increasing pressure to the piezoelectric crystal 208 as the ambient temperature increases due to operation of the heater 414. The voltage across potentiometer 360 likewise increases to bias the electron tube 362 from its initial low conduction state into its high conduction state, thereby energizing the relay coil 224 to open the contacts 234 and 236 and thereby cause the gas valve to close the gas line 412 to extinquish the heater 414.

The ambient temperature will then start to drop in response to heater 414 being extinquished until a point is reached whereby the switch contacts 234 and 236 will automatically reset to their closed condition. At this time, the solenoid 406 will open the gas line 12 a1 lowing the fuel to reach the heater 414 and be burned therein, thereby repeating the heating cycle.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown on the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

switch means responsive to changes in the output signal of said piezoelectric crystal means.

2. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

control means operable in response to the signal from said piezoelectric crystal means and comprising a relay including a pair of switch contacts and a coil energized by the signal from the piezoelectric crystal means for controlling the actuation of said contacts between opened and closed positions.

3. The invention of claim 2 including reset means for said relay.

4. The invention of claim 3 wherein the switch contacts are actuated by an armature controlled by the coil, and wherein the reset means includes reed means on the armature and plunger means movable into contact with the reed means to reset the switch contacts.

5. The invention of claim 4 including a power receptacle for receiving a plug therein, and said plunger extending into said receptacle for actuation by insertion of the plug into the receptacle to effect the reset.

6. The invention of claim 2 including another coil in flux aiding relationship with said relay coil; and means for providing energization to said another coil.

7. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means haaving a curvature defined by one end fixed to said anchor means and a movalbe end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition;

means generating a voltage proportional to said signal from the piezoelectric crystal means, and amplifier means providing an output signal in response to said proportional voltage.

8. The invention of claim 7 including pressure means operable on said piezoelectric crystal means for establishing an initial signal level from said piezoelectric signal means.

9. The invention of claim 8 including means adjustably positioning said pressure means relative to said piezoelectric crystal means. I

10. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

thermal load means proximate said bimetal means.

11. The invention of claim 10 wherein said thermal load means comprise a pair of thermally conductive plate members.

12. The invention of claim 11 including means adjustably positioning said thermal load means relative to said bimetal means.

13. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

alarm means controlled by the signal from said piezoelectric crystal means providing an indication as to the occurrence of an excessive thermal condition.

14. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

means for transmitting pressure changes from said bimetal means to said piezoelectric crystal means comprising a somewhat flexible V-shaped bracket member.

15. A thermally responsive system comprising:

piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means;

arcuate, electrically conductive bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and

means establishing a current flow through said bimetal means whereby said bimetal means is responsive to heat generated therein by said current flow.

16. A system for protecting a load from excessive current therethrough comprising:

electrically conductive bimetal means in series with said load and having a portion movable in response to current flow therethrough;

piezoelectric crystal means contacting said movable portion of said bimetal means and capable of producing a signal in accordance with pressure applied thereto by said movable portion; and

means controlled by the signal from said piezoelectric crystal means for reducing the current through said load in response to the occurrence of excessive current therethrough.

17. The invention of claim 16 wherein the means for reducing load current includes a switch in series with said load which opens in response to the signal from said piezoelectric crystal achieving a particular value to terminate the flow of load current.

18. The invention of claim 17 including a coil energized by the signal from the piezoelectric crystal for opening said switch in response to the signal achieving said particular value.

19. The invention of claim 18 including an armature controlled by said coil for opening said switch, and reset means for reclosing said switch.

20. The invention of claim 19 wherein the reset means includes a reed attached to said armature and a plunger movable into contact with said reed for retracting the armature.

21. The invention of claim 20 including a power receptacle having a pair of contacts for energizing the load through a plug inserted therein, and means connecting said bimetal means in series with said contacts, said switch and the source of power for the load.

22. The invention of claim 21 wherein said reset plunger extends into said power receptacle and is operated by insertion of the plunger into the power receptacle to reset the switch and thereby complete the series circuit enabling current flow therein.

23. The invention of claim 16 including a thermal member located proximate said 'bimetal means, said thermal member acting as a thermal load to said bimetal means.

24. The invention of claim 23 including means adjustably positioning said thermal member relative to said bimetal means to thereby vary the thermal loading.

25. The invention of claim 16 including pressure means applying a predetermined initial pressure to said piezoelectric crystal to thereby cause an initial signal to be produced thereby.

26. The invention of claim 25 wherein said pressure means comprises at least one pressure plate, and adjustable means supporting said at least one pressure plate against said piezoelectric crystal.

27. The invention of claim 16 wherein said bimetal means includes an arcuate element having a pair of ends, with one end abutting said piezoelectric crystal and the other end fixedly anchored.

28. The invention of claim 18 including flux generating means proximate said coil for establishing an initial flux level for enabling actuation of said contacts.

29. The invention of claim 28 wherein said flux generating means comprises another coil, and including means for providing energization to said coil.

30. The invention of claim 18 including amplifier means responsive to the signal from said piezoelectric crystal for controlling the energization of said coil.

31. A system for protecting a load from excess current flow therethrough comprising:

a power receptacle including a pair of contacts for energizing the load through a plug connected therein;

switch means;

bimetal means including a portion movable in response to current flow therethrough;

means for connecting said switch means, bimetal means and power receptacle contacts in series across a power supply for the load; and piezoelectric crystal means contacting the movable portion of said bimetal means and generating a signal in accordance with pressure applied thereto by said bimetal means for controlling said switch 7 means to thereby reduce current flow through the load.

32. The invention of claim 31 wherein said switch means comprises a relay including a pair of switch contacts, an armature controlling said switch contacts, and a coil energized by the signal from the piezoelectric crystal for actuating said armature.

33. The invention of claim 32 including a reset plunger and flexible reed means on said armature and operable by said plunger to retract said armature thereby closing said switch means.

34. The invention of claim 33 wherein said plunger extends into said power receptacle and is operable to reset the switch means by the insertion of said plug into said receptacle.

35. The invention of claim 31 wherein said bimetal means comprises an arcuate element having a pair of ends, one end of which is fixed and the other being movable against said piezoelectric crystal. 

1. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and switch means responsive to changes in the output signal of said piezoelectric crystal means.
 2. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and control means operable in response to the signal from said piezoelectric crystal means and comprising a relay including a pair of switch contacts and a coil energized by the signal from the piezoelectric crystal means for controlling the actuation of said contacts between opened and closed positions.
 3. The invention of claim 2 including reset means for said relay.
 4. The invention of claim 3 wherein the switch contacts are actuated by an armature controlled by the coil, and wherein the reset means includes reed means on the armature and plunger means movable into contact with the reed means to reset the switch contacts.
 5. The invention of claim 4 including a power receptacle for receiving a plug therein, and said plunger extending into said receptacle for actuation by insertion of the plug into the receptacle to effect the reset.
 6. The invention of claim 2 including another coil in flux aiding relationship with said relay coil; and means for providing energization to said another coil.
 7. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means haaving a curvature defined by one end fixed to said anchor means and a movalbe end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; means generating a voltage proportional to said signal from the piezoelectric crystal means, and amplifier means providing an output signal in response to said proportional voltage.
 8. The invention of claim 7 including pressure means operable on said piezoelectric crystal means for establishing an initial signal level from said piezoelectric signal means.
 9. The invention of claim 8 including means adjustably positioning said pressure means relative to said piezoelectric crystal means.
 10. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with prEssure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and thermal load means proximate said bimetal means.
 11. The invention of claim 10 wherein said thermal load means comprise a pair of thermally conductive plate members.
 12. The invention of claim 11 including means adjustably positioning said thermal load means relative to said bimetal means.
 13. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and alarm means controlled by the signal from said piezoelectric crystal means providing an indication as to the occurrence of an excessive thermal condition.
 14. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and means for transmitting pressure changes from said bimetal means to said piezoelectric crystal means comprising a somewhat flexible V-shaped bracket member.
 15. A thermally responsive system comprising: piezoelectric crystal means producing an output signal in accordance with pressure applied thereto; anchor means disposed in spaced relation to said piezoelectric crystal means; arcuate, electrically conductive bimetal means having a curvature defined by one end fixed to said anchor means and a movable end restrained by said piezoelectric crystal means for applying pressure thereto in accordance with a tendency to vary curvature in response to variations of a thermal condition; and means establishing a current flow through said bimetal means whereby said bimetal means is responsive to heat generated therein by said current flow.
 16. A system for protecting a load from excessive current therethrough comprising: electrically conductive bimetal means in series with said load and having a portion movable in response to current flow therethrough; piezoelectric crystal means contacting said movable portion of said bimetal means and capable of producing a signal in accordance with pressure applied thereto by said movable portion; and means controlled by the signal from said piezoelectric crystal means for reducing the current through said load in response to the occurrence of excessive current therethrough.
 17. The invention of claim 16 wherein the means for reducing load current includes a switch in series with said load which opens in response to the signal from said piezoelectric crystal achieving a particular value to terminate the flow of load current.
 18. The invention of claim 17 including a coil energized by the signal from the piezoelectric crystal for opening said switch in response to the signal achieving said particular value.
 19. The invention of claim 18 including an armature controlled by said coil for opening said switch, and reset means for reclosing said switch.
 20. The invention of claim 19 wherein the reset means incluDes a reed attached to said armature and a plunger movable into contact with said reed for retracting the armature.
 21. The invention of claim 20 including a power receptacle having a pair of contacts for energizing the load through a plug inserted therein, and means connecting said bimetal means in series with said contacts, said switch and the source of power for the load.
 22. The invention of claim 21 wherein said reset plunger extends into said power receptacle and is operated by insertion of the plunger into the power receptacle to reset the switch and thereby complete the series circuit enabling current flow therein.
 23. The invention of claim 16 including a thermal member located proximate said bimetal means, said thermal member acting as a thermal load to said bimetal means.
 24. The invention of claim 23 including means adjustably positioning said thermal member relative to said bimetal means to thereby vary the thermal loading.
 25. The invention of claim 16 including pressure means applying a predetermined initial pressure to said piezoelectric crystal to thereby cause an initial signal to be produced thereby.
 26. The invention of claim 25 wherein said pressure means comprises at least one pressure plate, and adjustable means supporting said at least one pressure plate against said piezoelectric crystal.
 27. The invention of claim 16 wherein said bimetal means includes an arcuate element having a pair of ends, with one end abutting said piezoelectric crystal and the other end fixedly anchored.
 28. The invention of claim 18 including flux generating means proximate said coil for establishing an initial flux level for enabling actuation of said contacts.
 29. The invention of claim 28 wherein said flux generating means comprises another coil, and including means for providing energization to said coil.
 30. The invention of claim 18 including amplifier means responsive to the signal from said piezoelectric crystal for controlling the energization of said coil.
 31. A system for protecting a load from excess current flow therethrough comprising: a power receptacle including a pair of contacts for energizing the load through a plug connected therein; switch means; bimetal means including a portion movable in response to current flow therethrough; means for connecting said switch means, bimetal means and power receptacle contacts in series across a power supply for the load; and piezoelectric crystal means contacting the movable portion of said bimetal means and generating a signal in accordance with pressure applied thereto by said bimetal means for controlling said switch means to thereby reduce current flow through the load.
 32. The invention of claim 31 wherein said switch means comprises a relay including a pair of switch contacts, an armature controlling said switch contacts, and a coil energized by the signal from the piezoelectric crystal for actuating said armature.
 33. The invention of claim 32 including a reset plunger and flexible reed means on said armature and operable by said plunger to retract said armature thereby closing said switch means.
 34. The invention of claim 33 wherein said plunger extends into said power receptacle and is operable to reset the switch means by the insertion of said plug into said receptacle.
 35. The invention of claim 31 wherein said bimetal means comprises an arcuate element having a pair of ends, one end of which is fixed and the other being movable against said piezoelectric crystal. 